Print Head, Liquid Ejection Apparatus, And Piezoelectric Element Control Circuit

ABSTRACT

A print head includes a piezoelectric element that includes a first electrode supplied with a drive signal and a second electrode supplied with a reference voltage signal and is displaced by a difference in electric potential between the first electrode and the second electrode, a cavity that is filled with a liquid ejected from a nozzle along with the displacement of the piezoelectric element, a vibration plate that is disposed between the cavity and the piezoelectric element, a switch circuit that switches between supplying and not supplying the drive signal to the first electrode, and a low pass filter circuit that is electrically connected in parallel with the switch circuit.

This application claims priority to Japanese Patent Application No.2018-057646 filed on Mar. 26, 2018. The entire disclosure of JapanesePatent Application No. 2018-057646 is hereby incorporated herein byreference.

BACKGROUND 1. Technical Field

The present invention relates to a print head, a liquid ejectionapparatus, and a piezoelectric element control circuit.

2. Related Art

In an ink jet printer (liquid ejection apparatus) that prints an imageor a document by ejecting a liquid such as ink, it is known that apiezoelectric element such as a piezo element is used as a driveelement. The piezoelectric element is disposed in a print head incorrespondence with a plurality of nozzles ejecting ink and a cavityretaining ink ejected from the nozzle. By displacing the piezoelectricelement in accordance with a drive signal, a vibration plate disposedbetween the piezoelectric element and the cavity is bent, and thecapacity of the cavity is changed.

Accordingly, a predetermined amount of ink is ejected from the nozzle ata predetermined timing, and a dot is formed on a medium.

JP-A-2002-273874, JP-A-2002-283567, JP-A-2002-283565, JP-A-2002-264325,JP-A-2003-072069, and JP-A-2007-125732 disclose a liquid ejectionapparatus that controls displacement of a piezoelectric element andejects ink corresponding to the displacement of the piezoelectricelement by controlling whether or not to cause a selection circuit(switch circuit) to supply a drive signal to the piezoelectric elementwhich is displaced based on a difference in electric potential betweenan upper electrode and a lower electrode. Specifically,JP-A-2002-273874, JP-A-2002-283567, JP-A-2002-283565, JP-A-2002-264325,JP-A-2003-072069, and JP-A-2007-125732 disclose a liquid ejectionapparatus that supplies a drive signal to an upper electrode by settinga switch circuit to be in a conduction state and stops supplying thedrive signal to the upper electrode by setting the switch circuit to bein a non-conduction state.

In the liquid ejection apparatus that ejects ink based on thedisplacement of the piezoelectric element as disclosed inJP-A-2002-273874, JP-A-2002-283567, JP-A-2002-283565, JP-A-2002-264325,JP-A-2003-072069, and JP-A-2007-125732, the supply of the drive signalto the upper electrode of the piezoelectric element is blocked in a casewhere the switch circuit is controlled to be in the non-conductionstate. In such a state where the supply of the drive signal is blockedby the switch circuit, a voltage supplied to the piezoelectric elementis ideally maintained at a voltage immediately before the switch circuitis controlled to be in the non-conduction state.

However, in actuality, a leakage current of the switch circuit orexogenous noise or the like accumulates electric charges in the upperelectrode of the piezoelectric element. The electric potential of theupper electrode is likely to be unstable. In a case where unintendedelectric charges are accumulated in the upper electrode of thepiezoelectric element, an unintended voltage occurs in the upperelectrode of the piezoelectric element. Consequently, the piezoelectricelement may be unintentionally displaced.

In a case where the piezoelectric element is unintentionally displaced,a vibration plate is also displaced based on the displacement.Consequently, the vibration plate is unintentionally bent, andunintended stress is exerted on the vibration plate. In a case wheresuch unintended stress occurring in the vibration plate is continuouslyexerted for a long time, stress is concentrated around a contact pointbetween the vibration plate and the cavity, and a crack or the like mayoccur in the vibration plate.

In addition, in a state where the vibration plate is unintentionallybent, a load that is higher than needed is exerted on the vibrationplate in a case where a transition is made to an ejection operation bycontrolling the switch circuit to be in the conduction state.Consequently, a crack or the like may occur in the vibration plate.

In a case where a crack occurs in the vibration plate, the ink retainedin the cavity leaks from the crack, and the amount of ejected ink variesdue to a change in the capacity of the cavity. Consequently, theaccuracy of ink ejection deteriorates.

Furthermore, in a case where ink leaking from the crack adheres to bothof the upper electrode and the lower electrode of the piezoelectricelement, a current path is formed between the upper electrode and thelower electrode through the ink. Consequently, the electric potential ofa reference voltage signal supplied to the lower electrode is changed.In a case where the reference voltage signal is supplied to a pluralityof piezoelectric elements in common, a change in the electric potentialof the reference voltage signal affects the displacement of theplurality of piezoelectric elements. That is, not only the accuracy ofejection from the nozzle corresponding to the vibration plate having thecrack is affected, but also the accuracy of ink ejection in the wholeliquid ejection apparatus may be affected.

The above concerns caused by an unstable voltage supplied to one end ofthe piezoelectric element are novel and are not disclosed in any ofJP-A-2002-273874, JP-A-2002-283567, JP-A-2002-283565, JP-A-2002-264325,JP-A-2003-072069, and JP-A-2007-125732.

SUMMARY

According to an aspect of the invention, there is provided a print headincluding a piezoelectric element that includes a first electrodesupplied with a drive signal and a second electrode supplied with areference voltage signal and is displaced by a difference in electricpotential between the first electrode and the second electrode, a cavitythat is filled with a liquid ejected from a nozzle along with thedisplacement of the piezoelectric element, a vibration plate that isdisposed between the cavity and the piezoelectric element, a switchcircuit that switches between supplying and not supplying the drivesignal to the first electrode, and a low pass filter circuit that iselectrically connected in parallel with the switch circuit.

In the print head, the piezoelectric element may be displaced such thatthe liquid is not ejected from the nozzle, based on the drive signalsupplied to the first electrode after passing through the low passfilter circuit.

In the print head, a plurality of the piezoelectric elements may beprovided, and the low pass filter circuit and the switch circuit may bedisposed for each of the plurality of piezoelectric elements.

In the print head, the switch circuit and the low pass filter circuitmay be disposed in an integrated circuit device.

In the print head, a resistance component when the switch circuit is inan OFF state may be smaller than a resistance component of thepiezoelectric element.

According to another aspect of the invention, there is provided a liquidejection apparatus including a drive circuit that outputs a drivesignal, a piezoelectric element that includes a first electrode suppliedwith the drive signal and a second electrode supplied with a referencevoltage signal and is displaced by a difference in electric potentialbetween the first electrode and the second electrode, a cavity that isfilled with a liquid ejected from a nozzle along with the displacementof the piezoelectric element, a vibration plate that is disposed betweenthe cavity and the piezoelectric element, a switch circuit that switchesbetween supplying and not supplying the drive signal to the firstelectrode, and a low pass filter circuit that is electrically connectedin parallel with the switch circuit.

In the liquid ejection apparatus, the piezoelectric element may bedisplaced such that the liquid is not ejected from the nozzle, based onthe drive signal supplied to the first electrode after passing throughthe low pass filter circuit.

In the liquid ejection apparatus, a plurality of the piezoelectricelements may be provided, and the low pass filter circuit and the switchcircuit may be disposed for each of the plurality of piezoelectricelements.

In the liquid ejection apparatus, the switch circuit and the low passfilter circuit may be disposed in an integrated circuit device.

In the liquid ejection apparatus, a resistance component when the switchcircuit is in an OFF state may be smaller than a resistance component ofthe piezoelectric element.

According to still another aspect of the invention, there is provided apiezoelectric element control circuit controlling a piezoelectricelement of a print head including the piezoelectric element thatincludes a first electrode supplied with a drive signal and a secondelectrode supplied with a reference voltage signal and is displaced by adifference in electric potential between the first electrode and thesecond electrode, a cavity that is filled with a liquid ejected from anozzle along with the displacement of the piezoelectric element, and avibration plate that is disposed between the cavity and thepiezoelectric element. The piezoelectric element control circuitincludes a switch circuit that switches between supplying and notsupplying the drive signal to the first electrode, and a low pass filtercircuit that is electrically connected in parallel with the switchcircuit.

In the piezoelectric element control circuit, the drive signal afterpassing through the low pass filter circuit may displace thepiezoelectric element such that the liquid is not ejected from thenozzle.

In the piezoelectric element control circuit, the print head may furtherinclude a plurality of the piezoelectric elements, and the low passfilter circuit and the switch circuit may be disposed for each of theplurality of piezoelectric elements.

In the piezoelectric element control circuit, the switch circuit and thelow pass filter circuit may be disposed in an integrated circuit device.

In the piezoelectric element control circuit, a resistance componentwhen the switch circuit is in an OFF state may be smaller than aresistance component of the piezoelectric element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view illustrating a schematic configuration of aliquid ejection apparatus.

FIG. 2 is a block diagram illustrating an electrical configuration ofthe liquid ejection apparatus.

FIG. 3 is a flowchart for describing a mode transition in each operationmode of the liquid ejection apparatus.

FIG. 4 is a sectional view illustrating a schematic configuration of anejection unit.

FIG. 5 is a diagram illustrating one example of arrangement of anejection module and a plurality of nozzles disposed in the ejectionmodule.

FIGS. 6A-C are diagrams for describing a relationship betweendisplacement of a piezoelectric element and a vibration plate andejection.

FIG. 7 is a diagram illustrating one example of a drive signal in aprinting mode.

FIG. 8 is a block diagram illustrating an electrical configuration ofthe ejection module and a drive IC.

FIG. 9 is a diagram illustrating a decoding content in a decoder.

FIG. 10 is a diagram for describing operation of the drive IC in theprinting mode.

FIGS. 11A-B are diagrams schematically illustrating the displacement ofthe piezoelectric element and the vibration plate in a case where avoltage value of an electrode of the piezoelectric element is increased.

FIG. 12 is a circuit diagram illustrating an electrical configuration ofa selection circuit.

FIG. 13 is a diagram illustrating a relationship between the drivesignal and a drive signal in the printing mode.

FIG. 14 is a diagram illustrating a relationship between the drivesignal and the drive signal in a standby mode and a sleep mode.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an exemplary embodiment of the invention will be describedusing the drawings. The drawings are used for convenience ofdescription. The embodiment described below does not unduly limit thecontent of the invention disclosed in the claims. In addition, not allconfigurations described below are essential constituents of theinvention.

Hereinafter, a liquid ejection apparatus that includes a print headaccording to the invention will be described with an example as an inkjet printer that is a printing apparatus ejecting ink as a liquid.

The liquid ejection apparatus can be exemplified by, for example, aprinting apparatus such as an ink jet printer, a coloring materialejection apparatus used for manufacturing a color filter of a liquidcrystal display and the like, an electrode material ejection apparatusused for forming an electrode of an organic EL display, asurface-emitting display, and the like, and a bio-organic matterejection apparatus used for manufacturing a biochip.

1 Configuration of Liquid Ejection Apparatus

A printing apparatus as one example of the liquid ejection apparatusaccording to the embodiment is an ink jet printer that forms a dot on aprinting medium such as paper and prints an image including a character,a figure, and the like corresponding to the image data by ejecting inkdepending on image data supplied from an external host computer.

FIG. 1 is a perspective view illustrating a schematic configuration of aliquid ejection apparatus 1. FIG. 1 illustrates a direction X in which amedium P is transported, a direction Y that intersects with thedirection X and is a direction in which a moving object 2 reciprocates,and a direction Z in which ink is ejected. In the embodiment, thedirection X, the direction Y, and the direction Z will be described asaxes that are orthogonal to each other.

As illustrated in FIG. 1, the liquid ejection apparatus 1 includes themoving object 2 and a moving mechanism 3 that causes the moving object 2to reciprocate in the direction Y.

The moving mechanism 3 includes a carriage motor 31 as a drive source ofthe moving object 2, a carriage guide shaft 32 with its both ends fixed,and a timing belt 33 that extends almost parallel to the carriage guideshaft 32 and is driven by the carriage motor 31.

A carriage 24 included in the moving object 2 is supported by thecarriage guide shaft 32 in a manner capable of reciprocating and isfixed at a part of the timing belt 33. Thus, by driving the timing belt33 using the carriage motor 31, the moving object 2 is guided by thecarriage guide shaft 32 and reciprocates in the direction Y.

A print head 20 is disposed in a part of the moving object 2 facing themedium P. The print head 20 includes multiple nozzles. Ink is ejectedfrom each nozzle in the direction Z. In addition, the print head 20 issupplied with a control signal and the like through a flexible cable190.

The liquid ejection apparatus 1 includes a transport mechanism 4 thattransports the medium P in the direction X onto a platen 40. Thetransport mechanism 4 includes a transport motor 41 as a drive sourceand a transport roller 42 that is rotated by the transport motor 41 andtransports the medium P in the direction X.

At a timing at which the medium P is transported by the transportmechanism 4, the print head 20 ejects ink to the medium P, therebyforming an image on the surface of the medium P.

FIG. 2 is a block diagram illustrating an electrical configuration ofthe liquid ejection apparatus 1.

As illustrated in FIG. 2, the liquid ejection apparatus 1 includes acontrol unit 10 and the print head 20. In addition, the control unit 10and the print head 20 are connected through the flexible cable 190.

The control unit 10 includes a control circuit 100, a carriage motordriver 35, a transport motor driver 45, a drive circuit 50, and avoltage generation circuit 90.

The control circuit 100 supplies a plurality of control signals and thelike for controlling various configurations based on the image datasupplied from the host computer.

Specifically, the control circuit 100 supplies a control signal CTR1 tothe carriage motor driver 35. The carriage motor driver 35 drives thecarriage motor 31 in accordance with the control signal CTR1.Accordingly, movement of the carriage 24 illustrated in FIG. 1 in thedirection Y is controlled.

In addition, the control circuit 100 supplies a control signal CTR2 tothe transport motor driver 45. The transport motor driver 45 drives thetransport motor 41 in accordance with the control signal CTR2.Accordingly, movement of the medium P in the direction X by thetransport mechanism 4 illustrated in FIG. 1 is controlled.

In addition, the control circuit 100 supplies a clock signal SCK, aprinting data signal SI, a latch signal LAT, a change signal CH, and anoperation mode signal MC to the print head 20.

In addition, the control circuit 100 supplies a drive data signal dA tothe drive circuit 50.

The voltage generation circuit 90 generates, for example, a voltage VHVof DC 42 V and supplies the voltage VHV to the print head 20 and thedrive circuit 50.

The drive circuit 50 generates a drive signal COM by performing class Damplification on a signal based on the drive data signal dA to a voltagebased on the voltage VHV and supplies the drive signal COM to the printhead 20. In addition, the drive circuit 50 generates, for example, areference voltage signal VBS of DC 5 V stepped down from the voltage VHVand supplies the reference voltage signal VBS to the print head 20.

The print head 20 includes a drive IC 80 and an ejection module 21.

The drive IC 80 is supplied with the clock signal SCK, the printing datasignal SI, the latch signal LAT, the change signal CH, the operationmode signal MC, the voltage VHV, and the drive signal COM.

The drive IC 80 switches between selecting and not selecting the drivesignal COM in a predetermined period based on the clock signal SCK, theprinting data signal SI, the operation mode signal MC, the latch signalLAT, and the change signal CH. The drive signal COM selected by thedrive IC 80 is supplied to the ejection module 21 as a drive signalVOUT. For example, the voltage VHV is used for generating a high voltagelogic signal for selecting the drive signal COM.

The ejection module 21 includes a plurality of ejection units 600, eachof which includes a piezoelectric element 60.

The drive signal VOUT supplied to the ejection module 21 is supplied toone end of the piezoelectric element 60. In addition, the referencevoltage signal VBS is supplied to the other end of the piezoelectricelement 60. The piezoelectric element 60 is displaced depending on thedifference in electric potential between the drive signal VOUT and thereference voltage signal VBS. The amount of ink corresponding to thedisplacement is ejected from the ejection unit 600.

While the number of print heads 20 included in the liquid ejectionapparatus 1 is described as one in FIG. 2, a plurality of print heads 20may be included. In addition, while the number of ejection modules 21included in the print head 20 is described as one in FIG. 2, a pluralityof ejection modules 21 may be included. In addition, while the drivecircuit 50 is described as being included in the control unit 10 in FIG.2, the drive circuit 50 may be included outside the control unit 10 andmay be electrically connected to the control unit 10 through theflexible cable 190. That is, the drive circuit 50 may be disposed in thecarriage 24 illustrated in FIG. 1 and may be operated by supplying thedrive data signal dA to the drive circuit 50 through the flexible cable190.

The liquid ejection apparatus 1 described above includes a plurality ofoperation modes including a printing mode, a standby mode, and a sleepmode.

The printing mode is an operation mode in which printing can be executedby ejecting ink to the medium P based on the supplied image data. Thestandby mode is an operation mode in which printing can be executed fora short time at an electric power consumption reduced from that in theprinting mode in a case where image data is supplied. The sleep mode isan operation mode in which the electric power consumption can be furtherreduced from that in the standby mode.

The relationship between each operation mode included in the liquidejection apparatus 1 will be described using FIG. 3. FIG. 3 is aflowchart for describing a mode transition in each operation mode of theliquid ejection apparatus 1.

As illustrated in FIG. 3, in a case where the liquid ejection apparatus1 is powered up, the control circuit 100 controls the operation mode tothe standby mode (S110). The control circuit 100 determines whether ornot a predetermined time elapses from the transition to the standby mode(S120).

In a case where the predetermined time does not elapse (N in S120), thecontrol circuit 100 determines whether or not image data is supplied tothe liquid ejection apparatus 1 (S130).

In a case where image data is not supplied (N in S130), the standby modecontinues. In a case where image data is supplied (Y in S130), thecontrol circuit 100 controls the operation mode to the printing mode(S140). In a case where printing corresponding to the supplied imagedata is finished, the control circuit 100 controls the operation mode tothe standby mode (S110).

In addition, in a case where the predetermined time elapses (Y in S120),the control circuit 100 controls the operation mode to the sleep mode(S150).

After the transition is made to the sleep mode, the control circuit 100determines whether or not image data is supplied to the liquid ejectionapparatus 1 (S160).

In a case where image data is not supplied (N in S160), the sleep modecontinues. In a case where image data is supplied (Y in S160), thecontrol circuit 100 controls the operation mode to the printing mode(S140).

The liquid ejection apparatus 1 may include operation modes other thanthe above operation modes as the plurality of operation modes. Forexample, the liquid ejection apparatus 1 may include operation modessuch as a test printing mode for performing test printing on the mediumP and a stop mode for stopping operation due to ink depletion, defectivetransport of the medium P, and the like.

2 Configuration and Operation of Ejection Unit

Next, a configuration and operation of the ejection module 21 and theejection unit 600 will be described.

FIG. 4 is a sectional view illustrating a schematic configuration of theejection unit 600 taken by cutting the ejection module 21 such that thesectional view includes the ejection unit 600. As illustrated in FIG. 4,the ejection module 21 includes the ejection unit 600 and a reservoir641.

The reservoir 641 is disposed for each color of ink. Ink is introducedinto the reservoir 641 from a supply port 661.

The ejection unit 600 includes the piezoelectric element 60 a vibrationplate 621, a cavity 631, and a nozzle 651. The vibration plate 621 isdisposed between the cavity 631 and the piezoelectric element 60 and isdisplaced by the piezoelectric element 60 disposed on its upper surface.The vibration plate 621 functions as a diaphragm thatincreases/decreases the internal capacity of the cavity 631 filled withink. The nozzle 651 is an open hole unit that is disposed in a nozzleplate 632 and communicates with the cavity 631. The cavity 631 is filledwith ink and functions as a pressure chamber of which the internalcapacity is changed by displacement of the piezoelectric element 60. Thenozzle 651 communicates with the cavity 631 and ejects ink in the cavity631 in response to a change in the internal capacity of the cavity 631.

The piezoelectric element 60 illustrated in FIG. 4 has a structure inwhich a piezoelectric body 601 is interposed between a pair of a firstelectrode 611 and a second electrode 612. The first electrode 611 issupplied with the drive signal VOUT, and the second electrode 612 issupplied with the reference voltage signal VBS. In the piezoelectricelement 60 having such a structure, the center part of the piezoelectricbody 601 is displaced in an up-down direction with respect to both endparts of the piezoelectric body 601 along with the first electrode 611,the second electrode 612, and the vibration plate 621 depending on thedifference in electric potential between the first electrode 611 and thesecond electrode 612. Ink is ejected from the nozzle 651 along with thedisplacement of the piezoelectric element 60.

FIG. 5 is a diagram illustrating one example of arrangement of theejection module 21 and a plurality of nozzles 651 disposed in theejection module 21 in a case where the liquid ejection apparatus 1 isseen in a plan view in the direction Z. In FIG. 5, the print head 20 isdescribed as including four ejection modules 21.

As illustrated in FIG. 5, a nozzle array L that includes a plurality ofnozzles 651 disposed in an array form in a predetermined direction isdisposed in each ejection module 21. Each nozzle array L is formed by nnozzles 651 arranged in an array form in the direction X.

The nozzle array L illustrated in FIG. 5 is one example and may beconfigured in a different manner. For example, in each nozzle array L, nnozzles 651 may be arranged in a zigzag form such that even-numberednozzles 651 counted from the end are at different positions in thedirection Y from odd-numbered nozzles 651. In addition, each nozzlearray L may be formed in a direction different from the direction X. Inaddition, while the number of nozzle arrays L disposed in each ejectionmodule 21 is illustrated as “1” in the embodiment, “2” or more nozzlearrays L may be formed in each ejection module 21.

In the embodiment, n nozzles 651 forming the nozzle array L are disposedat a high density of 300 or more per one inch in the ejection module 21.Thus, in the ejection module 21, n piezoelectric elements 60 aredisposed at a high density in correspondence with n nozzles 651.

In addition, in the embodiment, it is preferable that the piezoelectricbody 601 used in the piezoelectric element 60 be a thin film having athickness of, for example, 1 μm or less. Accordingly, the amount ofdisplacement of the piezoelectric element 60 with respect to thedifference in electric potential between the first electrode 611 and thesecond electrode 612 can be increased.

An ejection operation for ink ejected from the nozzle 651 will bedescribed using FIGS. 6A-C. FIGS. 6A-C are diagrams for describing arelationship between displacement of the piezoelectric element 60 andthe vibration plate 621 and ejection in a case where the drive signalVOUT is supplied to the piezoelectric element 60. In FIG. 6A,displacement of the piezoelectric element 60 and the vibration plate 621in a case where a voltage Vc is supplied as the drive signal VOUT isschematically illustrated. In addition, in FIG. 6B, displacement of thepiezoelectric element 60 and the vibration plate 621 in a case where thevoltage value of the drive signal VOUT supplied to the piezoelectricelement 60 is controlled to approach the reference voltage signal VBSfrom the voltage Vc is schematically illustrated. In addition, in FIG.6C, displacement of the piezoelectric element 60 and the vibration plate621 in a case where the voltage value of the drive signal VOUT suppliedto the piezoelectric element 60 is controlled to further recede from thereference voltage signal VBS than the voltage Vc is schematicallyillustrated.

In the state of FIG. 6A, the piezoelectric element and the vibrationplate 621 are displaced depending on the difference in electricpotential between the drive signal VOUT supplied to the first electrode611 and the reference voltage signal VBS supplied to the secondelectrode 612. Specifically, the piezoelectric element 60 and thevibration plate 621 are bent in the direction Z. At this point, thefirst electrode 611 is supplied with the voltage Vc as the drive signalVOUT. As will be illustrated in FIG. 7, the voltage Vc is the voltagevalue at the start timing and the end timing of voltage waveforms Adp,Bdp, and Cdp constituting the drive signal COM. That is, the state ofthe piezoelectric element 60 and the vibration plate 621 illustrated inFIG. 6A is a reference state of the piezoelectric element 60 in theprinting mode.

In a case where the voltage value of the drive signal VOUT is controlledto approach the voltage value of the reference voltage signal VBS, thedisplacement of the piezoelectric element 60 and the vibration plate 621in the direction Z is reduced as illustrated in FIG. 6B. At this point,the internal capacity of the cavity 631 is increased, and ink is drawninto the cavity 631 from the reservoir 641.

Then, the voltage value of the drive signal VOUT is controlled to recedefrom the voltage value of the reference voltage signal VBS. At thispoint, as illustrated in FIG. 6C, the displacement of the piezoelectricelement 60 and the vibration plate 621 in the direction Z is increased.Accordingly, the internal capacity of the cavity 631 is decreased, andink filling the cavity 631 is ejected from the nozzle 651.

The ejection unit 600 is repeatedly set to be in the states of FIGS.6A-C by supplying the drive signal VOUT to the first electrode 611.Accordingly, ink is ejected from the nozzle 651, and a dot is formed onthe medium P. The displacement of the piezoelectric element 60 and thevibration plate 621 illustrated in FIGS. 6A-C is increased in thedirection Z as the difference in electric potential between the drivesignal VOUT supplied to the first electrode 611 and the referencevoltage signal VBS supplied to the second electrode 612 is increased.That is, the amount of ejection of ink ejected from the nozzle 651 iscontrolled depending on the difference in electric potential between thedrive signal VOUT and the reference voltage signal VBS.

The displacement of the piezoelectric element 60 and the vibration plate621 with respect to the drive signal VOUT illustrated in FIGS. 6A-C ismerely one example. For example, ink may be drawn into the cavity 631from the reservoir 641 in a case where the difference in electricpotential between the drive signal VOUT and the reference voltage signalVBS is large. Ink filling the cavity 631 may be ejected from the nozzle651 in a case where the difference in electric potential between thedrive signal VOUT and the reference voltage signal VBS is small.

3 Configuration and Operation of Drive IC

Next, a configuration and operation of the drive IC 80 that is anintegrated circuit device will be described.

First, one example of the drive signal COM supplied to the drive IC 80will be described using FIG. 7. Then, the configuration and operation ofthe drive IC 80 will be described using FIG. 8 to FIG. 10.

FIG. 7 is a diagram illustrating one example of the drive signal COM inthe printing mode. FIG. 7 illustrates a period T1 from a rise of thelatch signal LAT until a rise of the change signal CH, a period T2 afterthe period T1 until the subsequent rise of the change signal CH, and aperiod T3 after the period T2 until a rise of the latch signal LAT. Acycle that includes the periods T1, T2, and T3 is a cycle Ta of forminga new dot on the medium P.

As illustrated in FIG. 7, in the printing mode, the drive circuit 50generates the voltage waveform Adp in the period T1. In a case where thevoltage waveform Adp is supplied to the piezoelectric element 60, apredetermined amount of ink, specifically, approximately a medium amountof ink, is ejected from the corresponding ejection unit 600.

In addition, the drive circuit 50 generates the voltage waveform Bdp inthe period T2. In a case where the voltage waveform Bdp is supplied tothe piezoelectric element 60, approximately a small amount of inksmaller than the predetermined amount is ejected from the correspondingejection unit 600.

In addition, the drive circuit 50 generates the voltage waveform Cdp inthe period T3. In a case where the voltage waveform Cdp is supplied tothe piezoelectric element 60, the piezoelectric element 60 is displacedsuch that ink is not ejected from the corresponding ejection unit 600.Accordingly, a dot is not formed on the medium P. The voltage waveformCdp is a voltage waveform for preventing an increase in the viscosity ofink by applying micro-vibration to ink around the open hole unit of thenozzle of the ejection unit 600. In the following description,“micro-vibration” refers to displacement of the piezoelectric element 60that is performed such that ink is not ejected from the ejection unit600 in order to prevent an increase in the viscosity of ink.

Both of the voltage values at the start timing and the end timing of thevoltage waveform Adp, the voltage waveform Bdp, and the voltage waveformCdp are equal to the voltage Vc. That is, the voltage waveforms Adp,Bdp, and Cdp are voltage waveforms of which the voltage value starts atthe voltage Vc and ends at the voltage Vc. Accordingly, in the printingmode, the drive circuit 50 outputs the drive signal COM having a voltagewaveform in which the voltage waveforms Adp, Bdp, and Cdp areconsecutive in the cycle Ta.

By supplying the voltage waveform Adp in the period Tl and the voltagewaveform Bdp in the period T2 to the first electrode 611, approximatelya medium amount of ink and approximately a small amount of ink areejected from the ejection unit 600 in the cycle Ta. Accordingly, a“large dot” is formed on the medium P. In addition, by supplying thevoltage waveform Adp in the period T1 and not supplying the voltagewaveform Bdp in the period T2 to the first electrode 611, approximatelya medium amount of ink is ejected from the ejection unit 600 in thecycle Ta. Accordingly, a “medium dot” is formed on the medium P. Inaddition, by not supplying the voltage waveform Adp in the period T1 andsupplying the voltage waveform Bdp in the period T2 to the firstelectrode 611, approximately a small amount of ink is ejected from theejection unit 600 in the cycle Ta. Accordingly, a “small dot” is formedon the medium P. In addition, by not supplying the voltage waveforms Adpand Bdp in the periods T1 and T2 and supplying the voltage waveform Cdpin the period T3 to the first electrode 611, ink is not ejected from theejection unit 600 and is subjected to micro-vibration in the cycle Ta.In this case, a dot is not formed on the medium P.

Next, one example of the drive signal COM in the standby mode and thesleep mode will be described. Illustration is not provided for the drivesignal COM in the standby mode and the sleep mode.

In the case of the standby mode and the sleep mode, ink is not ejectedto the medium P. Thus, the periods T1, T2, and T3 are not defined.Accordingly, in the standby mode and the sleep mode, the latch signalLAT and the change signal CH are signals at L level.

In the standby mode, the drive circuit 50 controls the voltage value ofthe drive signal COM to approach the voltage value of the referencevoltage signal VBS.

In addition, the drive circuit 50 stops operating in the sleep mode. Thesituation in which the drive circuit 50 stops operating is a case wherethe drive circuit 50 is supplied with the drive data signal dA forstopping generation of the drive signal COM, and specifically, includesa situation in which the drive circuit 50 outputs the ground electricpotential as the drive signal COM.

In the standby mode, the reference voltage signal VBS outputs the samevoltage value as that in the printing mode. Accordingly, printing can beexecuted for a short time in a case where image data is supplied. Inaddition, in the sleep mode, the output of the reference voltage signalVBS is stopped, and a voltage signal having the ground electricpotential is output. Accordingly, the electric power consumption can befurther reduced than that in the standby mode.

FIG. 8 is a block diagram illustrating an electrical configuration ofthe ejection module 21 and the drive IC 80. As illustrated in FIG. 8,the drive IC 80 includes a selection control circuit 210 and apiezoelectric element control circuit 220.

The selection control circuit 210 is supplied with the clock signal SCK,the printing data signal SI, the latch signal LAT, the change signal CH,the operation mode signal MC, and the voltage VHV. In addition, in theselection control circuit 210, a set of a shift register 212 (S/R), alatch circuit 214, and a decoder 216 is disposed in correspondence witheach ejection unit 600. That is, the same number of sets of the shiftregister 212, the latch circuit 214, and the decoder 216 as the totalnumber n of ejection units 600 are disposed in the print head 20.

The shift register 212 temporarily holds printing data [SIH, SIL] of twobits included in the printing data signal SI for each correspondingejection unit 600.

Specifically, stages of the shift registers 212 corresponding in numberto the ejection units 600 are connected to each other in cascade, andthe printing data signal SI that is serially supplied is sequentiallytransferred to the subsequent stage in accordance with the clock signalSCK. In FIG. 8, for distinction purposes, the shift registers 212 aredescribed as a first stage, a second stage, . . . , an n-th stage inorder from an upstream side on which the printing data signal SI issupplied.

Each of n latch circuits 214 latches the printing data [SIH, SIL] heldin the corresponding shift register 212 at a rise of the latch signalLAT.

Each of n decoders 216 decodes the printing data [SIH, SIL] of two bitslatched by the corresponding latch circuit 214 and operation mode data[MCH, MCL] of two bits included in the operation mode signal MC andgenerates and outputs a selection signal S.

FIG. 9 is a diagram illustrating a decoding content in the decoder 216.

The printing data [SIH, SIL] of two bits, the operation mode data [MCH,MCL] of two bits, the latch signal LAT, and the change signal CH areinput into the decoder 216.

In the case of the printing mode in which the operation mode data [MCH,MCL] is equal to [1, 1], the decoder 216 outputs the selection signal Sat a logic level based on the printing data [SIH, SIL] in each of theperiods T1, T2, and T3 defined by the latch signal LAT and the changesignal CH.

Specifically, in a case where the printing data [SIH, SIL] in theprinting mode is equal to [1, 1] that defines the “large dot”, thedecoder 216 outputs the selection signal S at H level in the period T1,H level in the period T2, and L level in the period T3.

In addition, in a case where the printing data [SIH, SIL] in theprinting mode is equal to [1, 0] that defines the “medium dot”, thedecoder 216 outputs the selection signal S at H level in the period T1,L level in the period T2, and L level in the period T3.

In addition, in a case where the printing data [SIH, SIL] in theprinting mode is equal to [0, 1] that defines the “small dot”, thedecoder 216 outputs the selection signal S at L level in the period T1,H level in the period T2, and L level in the period T3.

In addition, in a case where the printing data [SIH, SIL] in theprinting mode is equal to [0, 0] that defines the “micro-vibration”, thedecoder 216 outputs the selection signal S at L level in the period T1,L level in the period T2, and H level in the period T3.

In addition, in the standby mode and the sleep mode, the decoder 216determines the logic level of the selection signal S regardless of theprinting data [SIH, SIL] and the periods T1, T2, and T3.

Specifically, in the case of the standby mode in which the operationmode data [MCH, MCL] is equal to [1, 0], the decoder 216 outputs theselection signal S at H level.

In addition, in the case of the sleep mode in which the operation modedata [MCH, MCL] is equal to [0, 0], the decoder 216 outputs theselection signal S at L level.

The logic level of the selection signal S is shifted to a high amplitudelogic level based on the voltage VHV by a level shifter, notillustrated.

The piezoelectric element control circuit 220 includes a plurality ofselection circuits 230.

The plurality of selection circuits 230 are disposed in correspondencewith the ejection units 600, respectively. That is, the number ofselection circuits 230 included in one print head 20 is the same as thetotal number n of ejection units 600 included in the print head 20. Eachselection circuit 230 is supplied with the selection signal S from thecorresponding decoder 216. The selection circuit 230 selects the drivesignal COM based on the selection signal S and supplies the drive signalCOM to the first electrode 611 of the piezoelectric element 60 as thedrive signal VOUT.

Specifically, in a case where the selection circuit 230 is supplied withthe selection signal S at H level, the selection circuit 230 outputs thedrive signal COM as the drive signal VOUT. In addition, in a case wherethe selection circuit 230 is supplied with the selection signal S at Llevel, the selection circuit 230 does not output the drive signal COM asthe drive signal VOUT. Details of the configuration and operation of theselection circuit 230 will be described below.

In the drive IC 80 described above, an operation of generating the drivesignal VOUT based on the drive signal COM and supplying the drive signalVOUT to the ejection unit 600 will be described using FIG. 10.

FIG. 10 is a diagram for describing the operation of the drive IC 80 inthe printing mode.

In the printing mode, the printing data signal SI is serially suppliedin synchronization with the clock signal SCK and is sequentiallytransferred in the shift register 212 corresponding to the ejection unit600. In a case where the supply of the clock signal SCK is stopped, theprinting data [SIH, SIL] corresponding to the ejection unit 600 is heldin each shift register 212. The printing data signal SI is supplied inan order corresponding to the ejection units 600 in the last n-th stage,. . . , the second stage, and the first stage of the shift registers212.

In a case where the latch signal LAT rises, each latch circuit 214latches the printing data [SIH, SIL] held in the corresponding shiftregister 212 at the same time. In FIG. 10, the printing data [SIH, SIL]latched by the latch circuits 214 corresponding to the first stage, thesecond stage, . . . , the n-th stage of the shift registers 212 aredenoted by LT1, LT2, . . . , LTn.

The decoder 216 outputs the selection signal S at a logic levelcomplying with the content illustrated in FIG. 9 in each of the periodsT1, T2, and T3 depending on the size of a dot defined in the latchedprinting data [SIH, SIL].

In a case where the printing data [SIH, SIL] is equal to [1, 1], theselection circuit 230 selects the voltage waveform Adp in the period T1,selects the voltage waveform Bdp in the period T2, and does not selectthe voltage waveform Cdp in the period T3 in accordance with theselection signal S. Consequently, the drive signal VOUT corresponding tothe large dot illustrated in FIG. 10 is supplied to the piezoelectricelement 60.

In addition, in a case where the printing data [SIH, SIL] is equal to[1, 0], the selection circuit 230 selects the voltage waveform Adp inthe period T1, does not select the voltage waveform Bdp in the periodT2, and does not select the voltage waveform Cdp in the period T3 inaccordance with the selection signal S. Consequently, the drive signalVOUT corresponding to the medium dot illustrated in FIG. 10 is suppliedto the piezoelectric element 60.

In addition, in a case where the printing data [SIH, SIL] is equal to[0, 1], the selection circuit 230 does not select the voltage waveformAdp in the period T1, selects the voltage waveform Bdp in the period T2,and does not select the voltage waveform Cdp in the period T3 inaccordance with the selection signal S. Consequently, the drive signalVOUT corresponding to the small dot illustrated in FIG. 10 is suppliedto the piezoelectric element 60.

In addition, in a case where the printing data [SIH, SIL] is equal to[0, 0], the selection circuit 230 does not select the voltage waveformAdp in the period T1, does not select the voltage waveform Bdp in theperiod T2, and selects the voltage waveform Cdp in the period T3 inaccordance with the selection signal S. Consequently, the drive signalVOUT corresponding to the micro-vibration illustrated in FIG. 10 issupplied to the piezoelectric element 60.

Printing is not performed in the standby mode and the sleep mode. Thus,in the standby mode and the sleep mode, not only the latch signal LATand the change signal CH described above but also the clock signal SCKand the printing data signal SI are signals at L level. Accordingly, theshift register 212 and the latch circuit 214 do not operate. Thus, asdescribed above, the decoder 216 in the standby mode and the sleep modedetermines the logic level of the selection signal S in accordance withthe operation mode signal MC and outputs the selection signal S.

In the case of the standby mode in which the operation mode data [MCH,MCL] is equal to [1, 0], the selection circuit 230 selects the drivesignal COM having a voltage value equal to the reference voltage signalVBS in accordance with the supplied selection signal S at H level.Consequently, the drive signal VOUT having a voltage value equal to thereference voltage signal VBS is supplied to the piezoelectric element60.

In addition, in the case of the sleep mode in which the operation modedata [MCH, MCL] is equal to [0, 0], the selection circuit 230 does notselect the drive signal COM as the drive signal VOUT in accordance withthe supplied selection signal S at L level. Consequently, thepiezoelectric element 60 is not supplied with the drive signal VOUT.

4 Cause and Concern about Unstable Electric Potential of PiezoelectricElement

As described above, in a case where the selection signal S in theembodiment is at L level, the selection circuit 230 does not select thedrive signal COM as the drive signal VOUT. In this case, in a case wherethe supply of the drive signal VOUT to the first electrode 611 isblocked in the selection circuit 230, the first electrode 611 ideallycontinues holding a voltage that is supplied immediately before theselection signal S is set to be at L level.

However, in actuality, the voltage held in the first electrode 611 maybe changed. The cause of a change in the voltage held in the firstelectrode 611 is exemplified by for example, occurrence of a leakagecurrent in the selection circuit 230 and the piezoelectric element andaccumulation of electric charges caused by the leakage current in thefirst electrode 611. In addition, electric charges generated byexogenous noise or the like may be held in the first electrode 611.Holding electric charges in the first electrode 611 changes the voltageof the first electrode 611.

Furthermore, in a case where the nozzles 651 are disposed at a highdensity of 300 or more per inch as illustrated in the embodiment, thepiezoelectric elements 60 corresponding to the nozzles 651 are alsodisposed at a high density. Thus, the electrode area of thepiezoelectric element 60 is decreased, and the resistance component ofthe piezoelectric element 60 is increased. Accordingly, discharging ofelectric charges accumulated in the first electrode 611 due to theleakage current or the exogenous noise or the like is hindered, and thevoltage of the first electrode 611 of the piezoelectric element 60 maylikely become unstable.

As described above, accumulation of electric charges in the firstelectrode 611 changes the held voltage and makes the voltage of thefirst electrode 611 unstable. In a case where the voltage of the firstelectrode 611 is unstable, an unintended voltage is generated in thefirst electrode 611, and the piezoelectric element 60 may beunintentionally displaced.

FIGS. 11A-B are diagrams schematically illustrating the displacement ofthe piezoelectric element 60 and the vibration plate 621 in a case wherea voltage is increased due to accumulation of electric charges in thefirst electrode 611. In FIGS. 11A-B, the sleep mode in which theselection signal S may be output at L level for a long period will bedescribed as an example. In FIG. 11A, the displacement of thepiezoelectric element 60 and the vibration plate 621 immediately after atransition to the sleep mode is illustrated. In addition, in FIG. 11B,the displacement of the piezoelectric element 60 and the vibration plate621 in a case where the electric potential of the first electrode 611 isincreased after a transition to the sleep mode is illustrated.

As illustrated in FIG. 11A, the piezoelectric element 60 immediatelyafter a transition to the sleep mode is displaced based on thedifference in electric potential between the voltage of the firstelectrode 611 and the voltage of the second electrode 612. At thispoint, a voltage immediately before a transition to the sleep mode isheld in the first electrode 611. That is, the voltage of the firstelectrode 611 immediately after a transition to the sleep mode is avoltage that is assumed to be held in the first electrode 611.Accordingly, the piezoelectric element 60 is displaced within an assumedrange. Similarly, the vibration plate 621 is displaced within an assumedrange. At this point, stress F1 within an assumed range occurs at acontact point a between the vibration plate 621 and the cavity 631.

While a case where the voltage of the first electrode 611 and thevoltage of the second electrode 612 immediately before a transition tothe sleep mode have different voltage values is illustrated in FIG. 11A,it is preferable that the voltage of the first electrode 611 and thevoltage of the second electrode 612 have equal voltage values. In thiscase, the piezoelectric element 60 and the vibration plate 621 are notdisplaced.

In a case where a voltage changes due to accumulation of unintendedelectric charges in the first electrode 611, and the difference inelectric potential between the voltage of the first electrode 611 andthe voltage of the second electrode 612 is increased, the displacementof the piezoelectric element 60 is increased, and the displacement ofthe vibration plate 621 is increased as illustrated in FIG. 11B. In thiscase, stress F2 that is more significant than assumed may occur at thecontact point a between the vibration plate 621 and the cavity 631.

In an operation mode such as the sleep mode that continues for a longtime, the stress F2 may be continuously exerted at the contact point aof the vibration plate 621 for a long time. Consequently, a crack mayoccur in the vibration plate 621. Furthermore, in a case where atransition is made to the printing mode in a state where the vibrationplate 621 is displaced further than assumed, a load that is higher thanneeded may be exerted on the vibration plate 621 along with thedisplacement of the piezoelectric element 60 at the time of ejectingink. Consequently, a crack may occur in the vibration plate 621.

In a case where a crack occurs in the vibration plate 621, ink fillingthe cavity 631 leaks from the crack. Thus, the amount of ejected ink mayvary due to a change in the internal capacity of the cavity 631.Consequently, the accuracy of ink ejection deteriorates.

In addition, in a case where ink leaking from the crack adheres to bothof the first electrode 611 and the second electrode 612, a current pathis formed between the first electrode 611 and the second electrode 612through the ink. Accordingly, the voltage value of the reference voltagesignal VBS supplied to the second electrode 612 may be changed. In theliquid ejection apparatus 1 illustrated in the embodiment, the referencevoltage signal VBS is supplied to a plurality of second electrodes 612in common. Thus, in a case where the voltage value of the referencevoltage signal VBS is changed, the displacement of a plurality ofpiezoelectric elements 60 is affected. Consequently, the ejectionaccuracy of the whole liquid ejection apparatus 1 may be affected.

5 Configuration of Piezoelectric Element Control Circuit

As described above, in a case where the selection circuit 230 issupplied with the selection signal S at L level and does not select thedrive signal COM as the drive signal VOUT, electric charges areaccumulated in the first electrode 611, and the voltage of the firstelectrode 611 may become unstable. Consequently, an unintendeddifference in electric potential may occur in the piezoelectric element60. In a case where an unintended difference in electric potentialoccurs in the piezoelectric element 60, the piezoelectric element 60 isunintentionally displaced.

In the liquid ejection apparatus 1 in the embodiment, instability of thevoltage of the first electrode 611 can be reduced even in a case wherethe drive signal COM is not selected as the drive signal VOUT in theplurality of selection circuits 230 included in the piezoelectricelement control circuit 220.

FIG. 12 is a circuit diagram illustrating an electrical configuration ofthe selection circuit 230.

The selection circuit 230 includes an inverter 232 (NOT circuit), atransfer gate 234, and a low pass filter circuit 236 (low pass filter(LPF)). As described above, the selection circuit 230 disposed in thedrive IC 80 is disposed in correspondence with each ejection unit 600including the piezoelectric element 60. Accordingly, the inverter 232(NOT circuit), the transfer gate 234, and the low pass filter circuit236 are also disposed in correspondence with each ejection unit 600including the piezoelectric element 60. In other words, the low passfilter circuit 236 and the transfer gate 234 are disposed for each ofthe plurality of piezoelectric elements 60.

The selection signal S output by the decoder 216 is supplied to apositive control terminal that is not marked with a circle in thetransfer gate 234. In addition, the selection signal S is logicallyinverted by the inverter 232 and is supplied to a negative controlterminal that is marked with a circle in the transfer gate 234. Inaddition, the drive signal COM is supplied to an input terminal of thetransfer gate 234, and the drive signal VOUT is supplied to the ejectionunit 600 from an output terminal of the transfer gate 234.

In a case where the selection signal S at H level is supplied from thedecoder 216, the input terminal and the output terminal of the transfergate 234 are conducted. Accordingly, the drive signal COM is selectedand output to the ejection unit 600 as the drive signal VOUT. Inaddition, in a case where the selection signal S at L level is suppliedfrom the decoder 216, the input terminal and the output terminal of thetransfer gate 234 are set to be not conducted. Accordingly, the drivesignal COM is not selected as the drive signal VOUT. The transfer gate234 functions as a switch circuit that switches between supplying andnot supplying the drive signal COM to the piezoelectric element 60. Inthe following description, a state where the input terminal and theoutput terminal of the transfer gate 234 are conducted may be referredto as an ON state of the transfer gate 234. In addition, a state wherethe input terminal and the output terminal of the transfer gate 234 arenot conducted may be referred to as an OFF state of the transfer gate234.

The low pass filter circuit 236 is electrically connected between theinput terminal and the output terminal of the transfer gate 234. Inother words, the low pass filter circuit 236 is electrically connectedin parallel with the transfer gate 234.

The configuration of the low pass filter circuit 236 is not particularlylimited. For example, the low pass filter circuit 236 may be a passivefilter configured with at least any of a resistor, a capacitor, and acoil, or may be an active filter in which an op-amp or the like is used.

The operation of the selection circuit 230 will be described using FIG.13 and FIG. 14. FIG. 13 is a diagram for describing a relationshipbetween the drive signal COM and the drive signal VOUT in the printingmode.

In a case where the decoder 216 outputs the selection signal Scorresponding to the “large dot” in the cycle Ta, the selection circuit230 selects each of the voltage waveforms Adp and Bdp in the periods T1and T2. Accordingly, the voltage waveforms Adp and Bdp are output as thedrive signal VOUT through the transfer gate 234.

In addition, the selection circuit 230 does not select the voltagewaveform Cdp in the period T3. Thus, the transfer gate 234 is controlledto be in the non-conduction state in the period T3. At this point, thevoltage waveform Cdp is output as the drive signal VOUT through the lowpass filter circuit 236. Thus, a high frequency component of the voltagewaveform Cdp output as the drive signal VOUT is cut by the low passfilter circuit 236. Accordingly, in the period T3, the voltage Vc thatis acquired by cutting the high frequency component of the voltagewaveform Cdp is output as the drive signal VOUT.

In a case where the decoder 216 outputs the selection signal Scorresponding to the “medium dot” in the cycle Ta, the selection circuit230 selects the voltage waveform Adp in the period T1. Accordingly, thevoltage waveform Adp is output as the drive signal VOUT through thetransfer gate 234.

In addition, the selection circuit 230 does not select the voltagewaveforms Bdp and Cdp in the periods T2 and T3. Thus, the transfer gate234 is controlled to be in the non-conduction state in the periods T2and T3. At this point, the voltage waveforms Bdp and Cdp are output asthe drive signal VOUT through the low pass filter circuit 236. Thus,high frequency components of the voltage waveforms Bdp and Cdp output asthe drive signal VOUT are cut by the low pass filter circuit 236.Accordingly, in the periods T2 and T3, the voltage Vc that is acquiredby cutting the high frequency components of the voltage waveforms Bdpand Cdp is output as the drive signal VOUT.

In a case where the decoder 216 outputs the selection signal Scorresponding to the “small dot” in the cycle Ta, the selection circuit230 selects the voltage waveform Bdp in the period T2. Accordingly, thevoltage waveform Bdp is output as the drive signal VOUT through thetransfer gate 234.

In addition, the selection circuit 230 does not select the voltagewaveforms Adp and Cdp in the periods T1 and T3. Thus, the transfer gate234 is controlled to be in the non-conduction state in the periods T1and T3. At this point, the voltage waveforms Adp and Cdp are output asthe drive signal VOUT through the low pass filter circuit 236. Thus,high frequency components of the voltage waveforms Adp and Cdp output asthe drive signal VOUT are cut by the low pass filter circuit 236.Accordingly, in the periods T1 and T3, the voltage Vc that is acquiredby cutting the high frequency components of the voltage waveforms Adpand Cdp is output as the drive signal VOUT.

In a case where the decoder 216 outputs the selection signal Scorresponding to the “micro-vibration” in the cycle Ta, the selectioncircuit 230 selects the voltage waveform Cdp in the period T3.Accordingly, the voltage waveform Cdp is output as the drive signal VOUTthrough the transfer gate 234.

In addition, the selection circuit 230 does not select the voltagewaveforms Adp and Bdp in the periods T1 and T2. Thus, the transfer gate234 is controlled to be in the non-conduction state in the periods T1and T2. At this point, the voltage waveforms Adp and Bdp are output asthe drive signal VOUT through the low pass filter circuit 236. Thus,high frequency components of the voltage waveforms Adp and Bdp output asthe drive signal VOUT are cut by the low pass filter circuit 236.Accordingly, in the periods T1 and T2, the voltage Vc that is acquiredby cutting the high frequency components of the voltage waveforms Adpand Bdp is output as the drive signal VOUT.

As described above, in a case where the transfer gate 234 is controlledto be in a conduction state, the drive signal COM supplied to theselection circuit 230 is output as the drive signal VOUT through thetransfer gate 234. In a case where the transfer gate 234 is controlledto be in a non-conduction state, the drive signal COM supplied to theselection circuit 230 is output as the drive signal VOUT through the lowpass filter circuit 236.

As illustrated in FIG. 13, in a case where the drive signal COM isoutput through the low pass filter circuit 236, the drive signal VOUTslightly changes with respect to the voltage Vc. Thus, the piezoelectricelement 60 is slightly displaced due to the change. Thus, a cutofffrequency of the low pass filter circuit 236 is set to be sufficientlylower than the frequency of the drive signal COM such that ink is notejected from the nozzle 651 by displacement of the piezoelectric element60 based on the change in voltage. Specifically, the cutoff frequency ofthe low pass filter circuit 236 may be set to be less than or equal to1/100 of the frequency of the drive signal COM or may be set to be lessthan or equal to 1 Hz.

In addition, the cutoff frequency of the low pass filter circuit 236 maybe set such that the displacement of the piezoelectric element 60 causedby a change of the drive signal VOUT with respect to the voltage Vccorresponds to the micro-vibration. Accordingly, an increase in theviscosity of ink can be further prevented.

FIG. 14 is a diagram for describing a relationship between the drivesignal COM and the drive signal VOUT in the standby mode and the sleepmode. While FIG. 14 illustrates a case where the “large dot” is ejectedas the drive signal VOUT in the printing mode before a transition to thestandby mode, the same applies to cases where the drive signal VOUTcorresponds to the “medium dot”, the “small dot”, and the“micro-vibration”. In addition, FIG. 14 illustrates a voltage Vbs as thevoltage value of the reference voltage signal VBS and a voltage GND asthe ground electric potential.

In a case where the operation mode transitions to the standby mode fromthe printing mode, the drive signal COM is controlled to approach thevoltage value of the reference voltage signal VBS. That is, in a casewhere a predetermined time elapses, the voltage value of the drivesignal COM becomes equal to the voltage Vbs.

In the standby mode, the decoder 216 outputs the selection signal S at Hlevel. Accordingly, the voltage Vbs corresponding to the voltage valueof the drive signal COM is output as the voltage value of the drivesignal VOUT.

In a case where the operation mode transitions to the sleep mode, thevoltage values of the drive signal COM and the reference voltage signalVBS become equal to the voltage GND having the ground electricpotential.

In the sleep mode, the decoder 216 outputs the selection signal S at Llevel. Accordingly, the voltage value of the drive signal COM is outputas the drive signal VOUT through the low pass filter circuit 236.

The sleep mode continues for a sufficiently long term with respect tothe cycle Ta of the drive signal COM. That is, the sleep mode continuesfor a sufficiently long term with respect to a cycle based on the cutofffrequency of the low pass filter circuit 236. Accordingly, in the sleepmode, the voltage value of the drive signal VOUT approaches the voltagevalue of the drive signal COM without being affected by the cutofffrequency of the low pass filter circuit 236. In other words, even in acase where the transfer gate 234 is controlled to be in the OFF state, avoltage supplied to the piezoelectric element 60 can be controlled basedon the drive signal COM.

As described above, in the liquid ejection apparatus 1 in theembodiment, the voltage supplied to the piezoelectric element 60 can becontrolled using the drive signal COM even in a case where the drivesignal COM is selected as the drive signal VOUT using the selectionsignal S, and even in a case where the drive signal COM is not selectedas the drive signal VOUT using the selection signal S. Accordingly, asituation in which the voltage supplied to the piezoelectric element 60changes and becomes unstable is reduced.

The selection circuit 230 described above controls the drive signal VOUTsupplied to the piezoelectric element 60 by selecting the drive signalCOM based on the selection signal S. That is, the piezoelectric element60 is controlled by the piezoelectric element control circuit 220 thatincludes the plurality of selection circuits 230.

6 Action and Effect

The selection circuit 230 disposed in the print head 20 of the liquidejection apparatus 1 according to the embodiment described aboveincludes the low pass filter circuit 236 that is connected in parallelwith the transfer gate 234. Accordingly, even in a case where thetransfer gate 234 is controlled to be in the OFF state, the firstelectrode 611 of the piezoelectric element 60 is supplied with the drivesignal COM through the low pass filter circuit 236. Accordingly, asituation in which the electric potential of the piezoelectric element60 becomes unstable is reduced.

Furthermore, in the liquid ejection apparatus 1 according to theembodiment, the drive signal VOUT supplied to the piezoelectric element60 through the low pass filter circuit 236 in the printing mode has thevoltage value at the start timing and the end timing of each of thevoltage waveforms Adp, Bdp, and Cdp included in the drive signal COM. Inother words, the voltage value of the LPF output signal LPF-Out is thevoltage value held in the piezoelectric element 60 in a case where theselection circuit 230 does not include the low pass filter circuit 236.Accordingly, a situation in which the voltage supplied to thepiezoelectric element 60 through the low pass filter circuit 236 in theprinting mode affects the accuracy of ink ejection is reduced.

As described above, in the liquid ejection apparatus 1 according to theembodiment, a situation in which the electric potential of thepiezoelectric element 60 becomes unstable can be reduced withoutdecreasing the accuracy of ink ejection.

In addition, in the liquid ejection apparatus 1 according to theembodiment, the print head 20 includes a plurality of sets of thetransfer gate 234, the low pass filter circuit 236, and thepiezoelectric element 60. The selection circuit 230 selects whether tosupply the supplied drive signal COM to the first electrode 611 throughthe transfer gate 234 or supply the supplied drive signal COM to thefirst electrode 611 through the low pass filter circuit 236. That is,even in a case where the plurality of ejection units 600 are included,the selection circuit 230 can control the plurality of piezoelectricelements 60 based on the electric potential of the drive signal COM.Thus, a dedicated wire for controlling the voltage of the piezoelectricelement 60 is not needed. Accordingly, the size of the drive IC 80 canbe decreased.

In addition, in the liquid ejection apparatus 1 in the embodiment, asituation in which the voltage of the piezoelectric element 60 becomesunstable is reduced by including the low pass filter circuit 236 inparallel with the transfer gate 234. Thus, a situation in which thevoltage of the piezoelectric element 60 becomes unstable is reduced in acase where the resistance component of the piezoelectric element 60 isincreased by disposing the nozzles 651 at a high density and becomesgreater than the resistance component in a case where the transfer gate234 is in the OFF state, in other words, even in a case where theresistance component in a case where the transfer gate 234 is in the OFFstate is smaller than the resistance component of the piezoelectricelement 60.

As described above, in the liquid ejection apparatus 1 in theembodiment, a situation in which the voltage of the piezoelectricelement 60 disposed in the print head 20 becomes unstable is reduced.Thus, accumulation of unintended electric charges in the piezoelectricelement 60 and unintended displacement of the piezoelectric element 60are reduced. Thus, occurrence of unintended displacement of thevibration plate 621 that is displaced along with the piezoelectricelement 60 is reduced. Accordingly, a crack or the like may less likelyoccur in the vibration plate 621.

7 Modification Example

While the voltage waveforms Adp, Bdp, and Cdp are described as beingconsecutively included in the drive signal COM in the embodiment, thedrive signal COM may not include the voltage waveform Cdp correspondingto the micro-vibration. As described above, in a case where the drivesignal COM passes through the low pass filter circuit 236 and is output,the drive signal VOUT slightly changes with respect to the voltage Vc.Accordingly, the voltage waveform Cdp can be replaced by setting thecutoff frequency of the low pass filter circuit 236 such that thedisplacement of the piezoelectric element 60 caused by the change involtage corresponds to the micro-vibration. Accordingly, the cycle Ta ofthe drive signal COM can be shortened. Thus, the accuracy of inkejection can be increased.

In addition, while a serial scan type (serial printing type) ink jetprinter that performs printing on the medium P by moving the print head20 is illustrated as the liquid ejection apparatus in the embodiment,the invention can also be applied to a line head type ink jet printerthat performs printing on a printing medium without moving a head.

The invention includes substantially the same configuration as theconfiguration described in the embodiment (for example, a configurationhaving the same function, the same method, and the same result or aconfiguration having the same advantage and the same effect). Theinvention also includes a configuration acquired by replacing anon-substantial part of the configuration described in the embodiment.The invention also includes a configuration that accomplishes the sameeffect or achieves the same advantage as the configuration described inthe embodiment. The invention also includes a configuration acquired byadding a known technology to the configuration described in theembodiment.

What is claimed is:
 1. A print head comprising: a piezoelectric elementthat includes a first electrode supplied with a drive signal and asecond electrode supplied with a reference voltage signal and isdisplaced by a difference in electric potential between the firstelectrode and the second electrode; a cavity that is filled with aliquid ejected from a nozzle along with the displacement of thepiezoelectric element; a vibration plate that is disposed between thecavity and the piezoelectric element; a switch circuit that switchesbetween supplying and not supplying the drive signal to the firstelectrode; and a low pass filter circuit that is electrically connectedin parallel with the switch circuit.
 2. The print head according toclaim 1, wherein the piezoelectric element is displaced such that theliquid is not ejected from the nozzle, based on the drive signalsupplied to the first electrode after passing through the low passfilter circuit.
 3. The print head according to claim 1, wherein aplurality of the piezoelectric elements are provided, and the low passfilter circuit and the switch circuit are disposed for each of theplurality of piezoelectric elements.
 4. The print head according toclaim 1, wherein the switch circuit and the low pass filter circuit aredisposed in an integrated circuit device.
 5. The print head according toclaim 1, wherein a resistance component when the switch circuit is in anOFF state is smaller than a resistance component of the piezoelectricelement.
 6. A liquid ejection apparatus comprising: a drive circuit thatoutputs a drive signal; a piezoelectric element that includes a firstelectrode supplied with the drive signal and a second electrode suppliedwith a reference voltage signal and is displaced by a difference inelectric potential between the first electrode and the second electrode;a cavity that is filled with a liquid ejected from a nozzle along withthe displacement of the piezoelectric element; a vibration plate that isdisposed between the cavity and the piezoelectric element; a switchcircuit that switches between supplying and not supplying the drivesignal to the first electrode; and a low pass filter circuit that iselectrically connected in parallel with the switch circuit.
 7. Theliquid ejection apparatus according to claim 6, wherein thepiezoelectric element is displaced such that the liquid is not ejectedfrom the nozzle, based on the drive signal supplied to the firstelectrode after passing through the low pass filter circuit.
 8. Theliquid ejection apparatus according to claim 6, wherein a plurality ofthe piezoelectric elements are provided, and the low pass filter circuitand the switch circuit are disposed for each of the plurality ofpiezoelectric elements.
 9. The liquid ejection apparatus according toclaim 6, wherein the switch circuit and the low pass filter circuit aredisposed in an integrated circuit device.
 10. The liquid ejectionapparatus according to claim 6, wherein a resistance component when theswitch circuit is in an OFF state is smaller than a resistance componentof the piezoelectric element.
 11. A piezoelectric element controlcircuit controlling a piezoelectric element of a print head includingthe piezoelectric element that includes a first electrode supplied witha drive signal and a second electrode supplied with a reference voltagesignal and is displaced by a difference in electric potential betweenthe first electrode and the second electrode, a cavity that is filledwith a liquid ejected from a nozzle along with the displacement of thepiezoelectric element, and a vibration plate that is disposed betweenthe cavity and the piezoelectric element, the piezoelectric elementcontrol circuit comprising: a switch circuit that switches betweensupplying and not supplying the drive signal to the first electrode; anda low pass filter circuit that is electrically connected in parallelwith the switch circuit.
 12. The piezoelectric element control circuitaccording to claim 11, wherein the drive signal after passing throughthe low pass filter circuit displaces the piezoelectric element suchthat the liquid is not ejected from the nozzle.
 13. The piezoelectricelement control circuit according to claim 11, wherein the print headincludes a plurality of the piezoelectric elements, and the low passfilter circuit and the switch circuit are disposed for each of theplurality of piezoelectric elements.
 14. The piezoelectric elementcontrol circuit according to claim 11, wherein the switch circuit andthe low pass filter circuit are disposed in an integrated circuitdevice.
 15. The piezoelectric element control circuit according to claim11, wherein a resistance component when the switch circuit is in an OFFstate is smaller than a resistance component of the piezoelectricelement.